1. Field of the Invention
The present invention relates to an apparatus and method for correcting convergence in a television, and more particularly, to an apparatus and method for ring spline correction, which is capable of accurately effecting the convergence at the outermost portion of a screen. The present application is based on Korean Patent Application No. 2000-2959 filed on Jan. 21, 2000, which is incorporated herein by reference.
2. Description of the Related Art
A projection television includes red (R), green (G), and blue (B) cathode-ray tubes (CRTs) for displaying R, G, and B color images to project the displayed images onto a screen. As shown in FIG. 1, the distance and angle between each of R, G, and B CRTs and the screen is different, and thus convergence needs to be controlled so that the R, G, and B color signals may focus on one point.
A typical convergence control is performed in such a way that the R and B color images converge around the G color image. Specifically, a cross hatch pattern generated by a pattern generator is applied to the R, G, and B CRTs to obtain images projected onto the screen. Then, the degree to which R, G, and B images projected onto the screen are misconverged is detected through a charge coupled device (CCD), and then convergence correction values for correcting drive voltages applied to a convergence yoke of the R, G, and B CRTs according to the detected degree of misconvergence is calculated. The calculated convergence correction values are then stored in a memory and convergence is controlled by the stored convergence correction values.
An example of convergence correction algorithms is a spline operation algorithm. To perform an operation according to a spline operation algorithm, three point values and a slope between two end points are needed. As shown in FIG. 2, to obtain convergence correction values at an interval A with a point {circle around (1)} corresponding to the outermost portion of a screen, information on a slope is not available. To solve this problem, virtual points x and y are set so that the x and y point values are equal to {circle around (1)} and {circle around (5)} point values, respectively, and the values of both intervals E and F are set to be equal. Thus, this allows for the operation of a slope between points {circle around (1)} and {circle around (5)}, and further a spline operation for calculating the convergence correction values.
However, in the case of using the conventional spline operation algorithm, the operation at both the outermost intervals of the screen results in an error between slopes obtained from virtual point values and real values to thereby degrade accuracy for the spline operation result. Furthermore, this causes misconvergence at the outermost portion of the screen, which lowers image quality.
To solve the above problems, it is an objective of the present invention to provide an apparatus and method for ring spline convergence that reduces errors of convergence correction values at the outermost points of a screen.
Accordingly, to achieve the above objectives, the present invention provides a ring spline convergence correction apparatus in a television including a microprocessor for performing an operation to output unknown coefficients of a convergence interpolation polynomial in each interval between two points having adjacent coordinates, assuming that coordinate values at control points of adjacent lines are continuous, a memory for temporarily storing the unknown coefficients output by the microprocessor, a position coordinate generator for performing a predetermined operation to output coordinate values of a predetermined function at the control point, and an operator for outputting convergence correction values interpolated by applying the coordinate values of the predetermined function output from the position coordinate generator and the unknown coefficients read from the memory to the convergence interpolation polynomial.
The present invention also provides a ring spline convergence correction method for use in a television, which includes the steps of: (a) performing a predetermined operation to output unknown coefficients of a convergence interpolation polynomial in each interval between two points having adjacent coordinates, assuming that the coordinate values of control points on adjacent lines are continuous; (b) performing a predetermined operation to output the coordinate values of the convergence control point; and (c) performing a ring spline operation to output an interpolated convergence correction value by applying the unknown coefficients output in the step (a) and the coordinate values output in the step (b) to the convergence interpolation polynomial.